Viruses are simple organisms that can completely overwhelm the host organism they infect. Many viruses are associated with disease or cancer, but although much research has focused on viruses the molecular biology of many viruses is still poorly understood. To understand the lifecycle of a virus it is necessary to understand how gene expression is controlled by the virus. The rapidly growing bacteriophage, T7, presents an unique system for studying gene expression in a genetically well characterized organism. The long term objectives of this project are to characterize the processes that control the expression of the T7 genome and to test the hypothesis that T7 immunity exhibited by E. coli containing an F plasmid may be due to the inhibition of T7 RNA polymerase. The study of gene expression in phage T7 is particularly attractive. Since many T7 and E. coli proteins can be easily purified, protein/protein or protein/DNA interactions that are involved in the control of T7 gene expression can be quantitatively studied. As data accumulate, it should be possible to propose a detailed mechanism of the enzymology of the control of T7 gene expression. In the short term it will be necessary to first examine the inter- action of T7 RNA polymerase with class II and class III promoters emphasizing the determination of structure/function relationships by site specific mutation, and the determination of DNA binding affinities, conformational isomerization rates, efficiencies of initiation, and kinetics of transcription by abortive initiations techniques. With this data base, it should then be possible to study the effects of accessory proteins such as T7 gene product 3.5 on the enzymatic function of T7 RNA polymerase and compare these results with the data obtained for T7 RNA polymerase alone. An understanding of these rudimentary processes would then allow the study of the more complex processes involved in the regulation of gene expression in bacteriophage T7.